In the related art, as a method of converting the alternating current voltage to the direct current voltage, two following methods are generally known.
The first method uses a diode bridge circuit and a smoothing capacitor. The diode bridge circuit performs full wave rectification on the alternating current from the AC power supply. The smoothing capacitor smoothes the direct current after the full wave rectification.
In the first method, even if the alternating current voltage is either positive or negative, the current always flows through a series circuit of two diodes. At this point, in two diodes, the electric power corresponding to the product of the current flowing through the diode and the voltage in a forward direction of the diode is lost.
In the second method, a power factor improvement converter (PFC) is interposed between the diode bridge circuit and the smoothing capacitor in the first method. The power factor improvement converter boosts the voltage of the direct current subjected to the full wave rectification in the diode bridge circuit.
In the second method, since the current flows through a series circuit of two diodes at the time of the full wave rectification, the electric power is also lost. In addition, since the current flows alternately through a field effect transistor (FET) configuring the power factor improvement converter and the diode, the electric power is further lost.
Additionally, in order to cause the waveform of the input current to be a sine wave, the power factor improvement converter is required to set the output voltage to be higher than the input voltage. However, the exemplary embodiments are not limited to the configuration in which the voltage required in the load is necessarily higher than the input voltage. In this case, a step-down converter is connected to the downstream of the power factor improvement converter. Then, the voltage boosted by the power factor improvement converter is stepped-down to a desired voltage. When stepping-down, the electric power is also lost. The entire power conversion apparatus has a three-stage configuration of the AC-DC conversion, the DC-DC (step-up) conversion, the DC-DC (step-down) conversion, and the electric power loss is shown as the product of these conversions. For example, if the efficiency for one stage is 0.95, the efficiency for three stages is 0.95×0.95×0.95=0.86. That is, even in the prominent conversion having 95% efficiency, the efficiency falls to 86% in a three-stage connection. In this manner, even if each of the conversion efficiencies is good, the conversion efficiency remarkably deteriorates by setting the conversion to be multi stage.
Recently, the public demand for power saving properties of electric apparatus is increased. At the same time, it is essential not to produce current harmonic noises so as not to negatively influence the external environment. Therefore, the compatibility of the conversion efficiency enhancement and the current harmonics suppressing function in the power conversion apparatus that supplies the electric power to the load is demanded.
JP-A-2007-110869 and JP-A-2008-295248 are examples of the related art.